A vacuum-assisted, countergravity casting apparatus using a gas permeable mold is described in the Chandley et al U.S. Pat. No. 4,340,108 issued July 20, 1982 and U.S. Pat. No. 4,606,396 issued Aug. 19, 1986. Typically, the casting apparatus includes a casting mold having a porous, gas permeable upper mold member (cope) and a lower mold member (drag) sealingly secured together at a common horizontal parting plane, a vacuum box confronting the gas permeable upper mold member and means for immersing the underside of the lower mold member in an underlying pool of melt (e.g., molten metal) while evacuating the vacuum box to draw the melt upwardly through one or more ingate passages in the lower mold member into one or more mold cavities formed between the upper and lower mold members. Typically, the upper and lower mold members comprise gas permeable, resin-bonded sand mold members which are self-supporting and adhesively secured (glued) together at the common parting plane to minimize leakage of the melt at the parting plane.
The vacuum box typically rests on the lower mold member (mold drag) and includes a bottom lip carrying a sealing gasket adapted for sealingly engaging an upwardly facing sealing surface formed on the lower mold member about the mold cavity. The lateral dimension of the lower mold member must be large enough to accommodate the upwardly facing, vacuum box-engaging sealing surface thereon.
Moreover, the vacuum box and the mold are typically held together by some type of mechanical clamping arrangement to compress the sealing gasket between the vacuum box bottom lip and the mold sealing surface; for example, as shown in U.S. Pat. Nos. 4,340,108; 4,616,691; 4,632,171 and 4,658,880. In these clamping arrangements, the lower mold member (mold drag) oftentimes includes a plurality of relatively complex, pick-up features, such as threaded lugs, threaded bores, slotted keyways, counterbores and the like, for engagement with the clamping mechanism. The lateral dimension of the lower mold member must be large enough to accommodate these pick-up features thereon.
Finally, as disclosed in the U.S. Pat. No. 4,745,962 an upstanding levee may be formed on the lower mold member (mold drag) about the parting line with the upper mold member so as to isolate the parting line from the melt and allow deeper mold immersion during countergravity casting. Use of such an upstanding levee on the lower mold member requires that the lateral mold dimension be sufficient to accommodate such a levee thereon.
Use of these aforementioned vacuum box-to-mold seal, vacuum box-to-mold clamp and mold levee arrangements has necessitated that the lateral mold dimension, especially the lateral dimension of the mold drag, be greater than is actually needed to accommodate the mold cavity in the drag. As a result, relatively large mold drags have been used in practicing the countergravity casting process and require large amounts of costly mold-making material (e.g., resin-bonded sand) during mold fabrication and yield large amounts of used mold-making material which must be disposed of after casting. Moreover, an unnecessarily large mold surface is caused to contact the melt, thereby causing the formation of an unnecessarily large amount of slag.
It is an object of this invention to provide a countergravity casting apparatus including a unique casting mold/vacuum box/pick-up arrangement that provides the necessary sealing of the vacuum box about the mold and the necessary support of the mold throughout a casting cycle and that permits a substantial reduction in the lateral dimension of the mold to thereby reduce the amount of costly mold-making material (e.g., resin-bonded sand) needed to fabricate the mold for casting and to be disposed of after casting.
It is another object of the invention to provide a countergravity casting apparatus including a unique casting mold/vacuum box/pick-up arrangement wherein the vacuum box includes laterally spaced apart walls sealingly engaged to pick-up members disposed along laterally spaced apart sides of the mold so as to allow substantial reduction in the lateral dimension of the mold.